[PATCH 3.14 09/84] arm64: errata: add module build workaround for erratum #843419

From: Greg Kroah-Hartman
Date: Tue Sep 29 2015 - 11:45:59 EST

3.14-stable review patch. If anyone has any objections, please let me know.


From: Will Deacon <will.deacon@xxxxxxx>

commit df057cc7b4fa59e9b55f07ffdb6c62bf02e99a00 upstream.

Cortex-A53 processors <= r0p4 are affected by erratum #843419 which can
lead to a memory access using an incorrect address in certain sequences
headed by an ADRP instruction.

There is a linker fix to generate veneers for ADRP instructions, but
this doesn't work for kernel modules which are built as unlinked ELF

This patch adds a new config option for the erratum which, when enabled,
builds kernel modules with the mcmodel=large flag. This uses absolute
addressing for all kernel symbols, thereby removing the use of ADRP as
a PC-relative form of addressing. The ADRP relocs are removed from the
module loader so that we fail to load any potentially affected modules.

Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/arm64/Kconfig | 16 ++++++++++++++++
arch/arm64/Makefile | 4 ++++
arch/arm64/kernel/module.c | 2 ++
3 files changed, 22 insertions(+)

--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -306,6 +306,22 @@ menu "CPU Power Management"

source "drivers/cpuidle/Kconfig"

+config ARM64_ERRATUM_843419
+ bool "Cortex-A53: 843419: A load or store might access an incorrect address"
+ depends on MODULES
+ default y
+ help
+ This option builds kernel modules using the large memory model in
+ order to avoid the use of the ADRP instruction, which can cause
+ a subsequent memory access to use an incorrect address on Cortex-A53
+ parts up to r0p4.
+ Note that the kernel itself must be linked with a version of ld
+ which fixes potentially affected ADRP instructions through the
+ use of veneers.
+ If unsure, say Y.

source "net/Kconfig"
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -34,6 +34,10 @@ comma = ,

CHECKFLAGS += -D__aarch64__

+ifeq ($(CONFIG_ARM64_ERRATUM_843419), y)
+CFLAGS_MODULE += -mcmodel=large
# Default value
head-y := arch/arm64/kernel/head.o

--- a/arch/arm64/kernel/module.c
+++ b/arch/arm64/kernel/module.c
@@ -330,12 +330,14 @@ int apply_relocate_add(Elf64_Shdr *sechd
ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 0, 21,
+#ifndef CONFIG_ARM64_ERRATUM_843419
overflow_check = false;
ovf = reloc_insn_imm(RELOC_OP_PAGE, loc, val, 12, 21,
overflow_check = false;

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